The invention relates to a process for suppressing foam formation in a bubble column reactor.
Bubble column reactors are typically a substantially vertical column into which are introduced a liquid and a gas which at reactor conditions are treated to obtain a desired product.
Foaming in chemical reactors, especially bubble column reactors, reduces the liquid volume available for desired reactions This is particularly well known in hydroconversion reactors, for example for hydrocracking of heavy crudes into light products such as naphthas and distillates. Also, foaming tendencies have been evident in coal liquefaction reactors of the bubble column type as in Fischer Tropsch reactors of certain types. A bubble column reactor which experiences foaming can result in up to 80% or more in the reactor volume being occupied by gas, and consequently at most only about 20% of the volume of the reactor is available for the desired conversion.
One known method for avoiding foaming is to add anti-foaming agents such as silicone oils, polyglycols and the like. However, these agents are cracked under the severe conditions present in the reactors. For example, in a hydrocracking reactor, anti-foaming agents are exposed to hydrogen pressures over 100 bar and temperatures of 140.degree. C. or higher. Anti-foaming agents tend to crack into different chemical products which contaminate the liquid and gas in the reactor. In addition to requiring more frequent catalyst replacement in the downstream hydrodesulfurization reactors, such cracking of anti-foaming agents also tends to increase the operating costs of the overall process.
Frye and Berg, J. Colloid Interface Sci., 127, (1), 222 (1989) have shown that non-wettable particles can be used to thin or reduce foam layers, and consequently reduce foam formation. According to Frye and Berg, the mechanism for accomplishing such foam thinning is related to capillary pressure Frye and Berg conclude that such capillary pressure considerations show that when a contact angle of the particle in the fluid is less than 90.degree., film rupture will not occur. Frye and Berg also indicate that for particles with continuous smooth shapes like spheres, discs, ellipsoids and rods, film rupture will occur only if the contact angle is greater than 90.degree..
The need remains for a process for suppressing foam which is effective without significantly increasing the cost of the process carried out in the bubble column reactor.
The need also remains for a process for reducing foam which does not result in additional materials added to the reactor which can be altered or cracked by the conditions in the reactor.
It is therefore the primary object of the present invention to provide a process for suppressing foam formation which is simple and inexpensive.
It is a further of the present invention to provide a process for suppressing foam formation which does not result in contamination of products from the reactors
It is a still further object of the present invention to provide a process for foam suppression which can be employed in the hydroconversion reactor without requiring excessive additional materials
Other objects and advantages of the present invention will appear hereinbelow